A filament yarn nonwoven fabric mainly formed from a thermoplastic resin shows a high tenacity in comparison with other nonwoven fabrics during the preparation of bags, lids of containers and the like, and can be laminated by heat bonding without using an adhesive. As a result, the nonwoven fabric can be efficiently worked, and used in a wide range of applications. However, in order to obtain a sufficient tenacity of the nonwoven fabric, a thermoplastic resin having a high melting point must be used. The thermal adhesivity of the resultant nonwoven fabric to a nonwoven fabric or a film for which a low melting point resin is used has been insufficient.
Furthermore, when a conventional filament yarn nonwoven fabric composed of a thermoplastic resin is required to have a filtering function, fine particles are leaked because gaps among yarns forming the nonwoven fabric are too large. In other words, the nonwoven fabric has a disadvantage in that the filtering function is poor. However, when the fabric weight of the nonwoven fabric is increased to improve the filtering function, the thickness of the nonwoven fabric is increased to make the heat-sealing function poor. Since the nonwoven fabric has the above disadvantage, it is difficult to make a bag or the like of the nonwoven fabric.
As conventional technologies, for example, Japanese Unexamined Patent Publication (Kokai) No. 2000-202011 proposes a deodorizing and dehumidifying sheet prepared by superimposing two sheets having air and light permeability, integrally contact bonding a plurality of sites to form an absorption chamber, and packing a deodorizing agent and a dehumidifying agent. The patent publication describes that the sheet is useful for a mattress and the like. However, the sheet has a disadvantage in that powder leakage occurs when the particles of a filled material are fine or the material may become a powder.
Furthermore, when bags are produced from a filament yarn nonwoven fabric composed of a thermoplastic resin by heat bonding, the nonwoven fabric is usually heated and contact bonded at temperatures of the melting point or higher of the thermoplastic resin forming the yarn. The production apparatus must therefore be operated in the bag-making step at high temperature over a long time. As a result, the production step has a disadvantage in that a thermoplastic resin is melted and sticks to the hot roll and hot plate heater to deteriorate the product quality, and that the working rate cannot be increased. Moreover, when the heat bonding temperature is lowered, a predetermined sealing tenacity cannot be obtained. As a result, the production step also has a disadvantage in that complicated temperature control must be conducted.
In order to solve such problems, Japanese Unexamined Patent Publication (Kokai) No. 2001-315239 discloses a nonwoven fabric having a structure in which a non-heat-sealing layer and a heat-sealing layer are laminated. However, because the non-heat-sealing layer and the heat-sealing layer are laminated by the bonding action of the low melting point component in the composite yarn used in the nonwoven fabric, the adhesivity is greatly influenced by the compatibility of the thermoplastic resins. As a result, peeling is likely to take place between the non-heat-sealing layer and the heat-sealing layer even when both layers are heat contact bonded at temperatures close to the melting point of the low melting point component, and they cannot be bonded in a completely melt-sticking state.
Furthermore, the low melting point component that is melted for the purpose of laminating the two layers strikes through the non-heat-sealing layer, and the nonwoven fabric has a disadvantage in that good one side heat-sealing properties cannot be obtained.
As explained above, no conventional filament yarn nonwoven fabric composed of a thermoplastic resin satisfies both the filtering function and the heat-sealing function. Therefore, a thermally adhesive laminated nonwoven fabric that shows improvements in both functions is desired.